We highlight fundamental differences in the models of light-matter interaction between the behavior of Fock state detection in free space versus optical cavities. To do so, we study the phenomenon of the resonance of detectors with Fock wave packets as a function of their degree of monochromaticity, the number of spatial dimensions, the linear or quadratic nature of the light-matter coupling, and the presence (or absence) of cavity walls in space. In doing so we show that intuition coming from quantum optics in cavities does not straightforwardly carry to the free-space case. For example, in ($3+1$) dimensions the detector response to a Fock wave packet will go to zero as the wave packet is made more and more monochromatic and in coincidence with the detector’s resonant frequency. This is so even though the energy of the free-space wave packet goes to the expected finite value of $\hslash \mathrm{\Omega }$ in the monochromatic limit. This is in contrast to the behavior of the light-matter interaction in a cavity (even a large one) where the probability of absorbing a Fock quantum is maximized when the quantum is more monochromatic at the detector’s resonance frequency. We trace this crucial difference to the fact that monochromatic Fock states are not normalizable in the continuum; thus physical Fock states need to be constructed out of normalizable wave packets whose energy density goes to zero in the monochromatic limit as they get spatially delocalized.

中文翻译：

---

是什么让粒子探测器点击

我们强调了自由空间中 Fock 状态检测行为与光腔中光-物质相互作用模型的根本差异。为此，我们研究了探测器与 Fock 波包的共振现象作为其单色度、空间维数、光-物质耦合的线性或二次性质以及存在（或不存在）的函数) 空间中的空腔壁。通过这样做，我们表明来自腔中量子光学的直觉并不能直接适用于自由空间的情况。例如，在 ($3+1$) 维度，随着波包变得越来越单色并与检测器的谐振频率一致，探测器对 Fock 波包的响应将变为零。即使自由空间波包的能量达到预期的有限值$\hslash \mathrm{\Omega }$在单色极限。这与腔（即使是大腔）中光-物质相互作用的行为形成对比，其中当量子在探测器的共振频率上更加单色时，吸收福克量子的概率最大化。我们将这一关键差异追溯到这样一个事实：单色 Fock 状态在连续体中不可归一化；因此物理 Fock 状态需要由可归一化的波包构建，当它们在空间上离域时，其能量密度在单色极限中变为零。